The present invention relates to derailleur type bicycles, exemplified by racing bicycles and mountain bicycles, and particularly relates to control of the drive chain in such bicycles.
Bicycles of the type described above contain a gear shifting mechanism which includes a derailleur that is operated by the rider to shift the drive chain from one sprocket wheel to another, to thereby vary the bicycle transmission ratio, i.e. the ratio between the rate of rotation of the pedals and the rate of rotation of the bicycle wheels.
Proper operation of the transmission requires that the chain be maintained under adequate tension at all times. For this purpose, existing derailleurs always include some form of chain tensioning component. Since derailleurs are mass produced, the tension setting must be selected in anticipation of use by an average rider under average conditions. However, there are situations where the designed chain tension is not adequate to the conditions at hand. The preset tension (preset for the average rider) in typical mass produced derailleurs may not be adequate for rough terrain, high speeds or "chainsuck" (when the chain catches on a front chainring and becomes jammed) conditions. Moreover, the preset tension may be not adequately prevent "chain slap" (when the chain slaps against the frame) which can damage the frame tubing or paint.